In the March 2019 episode of Inside Xbox, Xbox Game Studios announced not only that Halo: The Master Chief Collection is coming to the PC, and is not only coming to Steam (store page is already up) in addition to the Microsoft Store, but that it will now finally feature Halo: Reach instead of just the first four mainline Halo titles. Titles included in The Master Chief Collection will come in segments, with Halo: Reach being the first one to come out and the rest coming as time passes on. On the Xbox One, players who already own The Master Chief Collection will automatically get access to Reach's multiplayer portion but will have to purchase the singleplayer separately. Other outlets also report that Halo 3: ODST will also be included in this release.
This means Halo 3, ODST, Reach and 4 will have their PC debuts. Halo: Combat Evolved had a well-received PC port by Gearbox in 2003 and can still be played online thanks to an official patch from 2014, while Halo 2 was ported in 2007 supposedly as a Windows Vista exclusive, but the fans were fairly quick to make workarounds to run it on XP, and even then it was too little too late. Since then, the only release of the Halo IP on the "pure" PC platform was Halo Wars: Definitive Edition, while the UWP platform got Halo Wars 2 and spin-off titles Spartan Assault and Spartan Strike.